The final, or “last chance,” filter currently used in ink jet printers is made of a polypropylene mesh, with its primary function being to protect the nozzles of the printhead from contamination of dirt or other foreign particles. It is known that particles above 1.2 μm in size can enter the printhead and adversely affect the printhead. For example, the particles can block nozzles or cause jet ejection in a non-perpendicular direction.
The changes in pressure that occur, for example, during start up allow particles that have been trapped by the filter to reorient themselves, allowing them to pass through the filter in a process called shedding. In other industries requiring high purity liquids, prior art solutions don't use the last chance filter, but rather employ a fluid system with large flow of fluid continuously recirculating through a main filter, with only a small portion of this flow available for use. However, this solution does not address the pressure shock associated with bringing the system pressure up to jetting pressure, nor does it provide for an entire system flush following servicing. Additionally, the elimination of the last chance filter does not allow for the replacement of parts, such as the printhead module, as dirt introduced into the fluid lines when the part is replaced would not be filtered out before entering the printhead.
Diverter valves are known, see, for example, U.S. Pat. No. 6,408,882 issued to Smith on Jun. 25, 2002, but not used in the ink jet industry. U.S. Pat. No. 6,408,882 discloses a Y-shaped diverter valve wherein an actuator moves the valve spool so as to allow fluid communication between the main port and only one of two secondary valves. The quick change in valve position creates a pressure surge, which pulses back to the filter, resulting in shedding.
U.S. Pat. No. 3,605,810, issued to Moroney on Sep. 20, 1971, discloses a flow diverter valve to be used with a flow meter loop. To maintain flow rate across a meter, the valve directs fluid from the inlet port through a loop, which can be open to the outlet port. When the outlet port is closed, fluid in the loop pushes against a piston thereby actuating a meter.
Pre-existing diverter valves have several drawbacks. For example, conventional diverter valves shut off flow to one output before shifting flow to a second output, and do not open the second port at the same rate that the first port is being closed. Additionally, conventional diverter valves cannot be adjusted such that both outputs are open to enable some of the fluid to bypass. Furthermore, conventional diverter valves drag their seals across the port which can cause the seals to break down, thereby generating particles that could contaminate the nozzles, thereby reducing the lifetime of the printhead.
Accordingly, the need exists for a diverter valve that provides a constant rate of flow and reduces the likelihood of shedding.